1. Field of the Invention
The present invention relates to an endoscope shape detecting apparatus for detecting and displaying an insertion shape and the like of an endoscope inserted into a body cavity.
2. Description of the Related Art
In recent years, there has been used an endoscope shape detecting apparatus which detects a shape and the like of an endoscope inserted, for example, into a body cavity using a magnetic-field generating element and a magnetic-field detecting element, and displays the detected shape by display means.
For example, Japanese unexamined patent publication No. H08-107875 as a first conventional example discloses an apparatus which detects the shape of the endoscope using magnetic fields, and displays the detected shape of the endoscope.
In the apparatus, a plurality of magnetic-field generating elements disposed at a predetermined interval in an insertion portion of the endoscope which is inserted in a body are driven to generate magnetic fields therearound, and three-dimensional positions of the respective magnetic-field generating elements are detected by magnetic-field detecting elements disposed outside the body. Then, a curve continuously linking the detected three-dimensional positions of the respective magnetic-field generating elements is generated, and a three-dimensional shape image representing a model of the insertion portion is displayed by the display means.
An operator, for example, can have a grasp of the position and the insertion shape and the like of a distal end portion of the insertion portion inserted in a body by observing the shape image. This helps the operator smoothly perform the work of inserting the insertion portion into a target region, for example.
In a case where the magnetic fields are generated to detect the shape as described above, it is desirable to perform the shape detection in an environment with less noise which influences the position detection, in order to accurately perform the position detection and calculate the shape of insertion portion based on the position detection. In particular, a noise source of a driving frequency of alternating current signal for driving the magnetic-field generating elements has a great influence on a calculation result of the position detection.
Therefore, in Japanese unexamined patent publication No. 2003-245243 as a second conventional example, driving frequencies of alternating current signals for driving a plurality of magnetic-field generating elements are selectable, and noise detection means detects frequency components of the noise detected in a driving stop state in which the plurality of magnetic-field generating elements are not driven. In addition, the publication discloses an apparatus having a configuration in which the plurality of magnetic-field generating elements are driven based on the alternating current signals of the driving frequencies with less frequency components of the detected noise, and position detection is accurately performed in the environment with less noise.